Terrace tiles 100x100 laid with vacuum, stains

that does not look like the vacuum suction foot, but rather like the wetting/liquid for the suction foot. With the suction foot, the marks would be circular, ask the tiler about the liquid and clean the entire surface with it

Thank you, I will do that tomorrow as soon as he is here.

And please waterproof it no matter what they tell you that it would not be necessary.